The overall goal of this research is to improve the detection and characterization of breast cancer using conventional and dynamic Nuclear Magnetic Resonance (NMR) imaging in combination with injectable contrast media. In the proposed work, NMR imaging will be used to detect and quantify tumor angiogenesis. This work focuses on developing quantitative methodologies using ultra- fast Echo Planar imaging (EPI) before and during injection of contrast agent to eliminate the' non-specific causes of variations of enhancement pattern. That is, by measuring the T1 of the lesion and the arterial input function to the lesion, one can extract quantitative tissue hemodynamic parameters-blood volume and extraction-flow (EF) product-that will provide an increasingly specific marker for cancer. This research thus seeks to develop a "physiological" NMR study of the breast with little additional exam time beyond that required for a conventional, contrast-enhanced study. The first part of the research focuses on validating and optimizing these methods in animal models of implanted breast tumors. We propose, using NMR imaging, to measure the relevant water exchange times, T1, and arterial concentrations of agent in vivo, and use a multicompartment tissue model to calculate vascular volume, extracellular volume and EF. The latter phase of this research is a pilot patient study of the developed quantitative methods. This study will test the hypothesis is that the NMR-measured regional vascular volume and the EF product will correlate with vessel count determined histologically from surgical and/or core biopsy; and that quantification of the underlying NMR parameters will provide a critical improvement over existing NMR imaging methods. Ultimately, the goal of this work is to produce an increasingly sensitive and specific test for breast cancer.